function checkForInt(evt) {
	evt = ( evt ) ? evt : window.event;
	var charCode = ( evt.which ) ? evt.which : evt.keyCode
	return (charCode <= 31 || (charCode >= 48 && charCode <= 57))
}

function recalc() {

	var intCurrent = document.getElementById('calc_current').value;
	var intTarget = document.getElementById('calc_target').value;

	if( intCurrent != 0 && intTarget != 0 ) {

		var fltScale = Math.pow( ( intTarget / intCurrent ), (1 / 3));
		
		fltScale = Math.round( fltScale * 1000 ) / 1000;
		
		document.getElementById('calc_scale').value = fltScale;
		
	}
}